Rabble arm



March 10, 1931. F. A. FAHRENWALD 1,796,247

RABBLE ARM Filed om. 8, 1928 Patented Mar. 10, 1931 PATENT FFICE FRANK A, FAHRENWALD, OF CHICAGO, ILLINOIS RABBLE. ARM

Application led October 8, 1928. SerialNc. 311,110.

This invention relates-to rabble arms o-r stirring devices for use in furnaces in which ores, for instance, sulphide ores, are subjected tothe process of roasting as a step preliminary to the processl of reduction.

Practically all sulphide ores have to be subjectedV to some sort of roasting or sintering operation before they are finally reduced to their metallicf constituents, and this opera- !0 tion is carried on in so-me form of furnace which generally comprises a heating chamber with a rotating stirring device adapted to agitate the ore during its treatment, and commonly termed a ,rabble arm.7 Such a rabble arm preferably consistsof a central upstanding column carrying a member extending laterally therefrom at a level which causes said member (or projections carried thereby) to enter and stir up the mass of ore being roasted; the laterally extending member being in some cases separately produced i and detachably connected with thev column to facilitate replacement in cases of failure, and in other cases made integral with the column. n

Heretofore, in order to withstand the heat incident to the roasting operation, the column of the rabble arm Vhas had a construction which permits a cooling medium to circulate through it, and it has been found desirable in some instances to extend this cooling principle to the laterally extending member las well.

v But artificial cooling of such stirring devices lends complication to the equipment and is uneconomical in operation, not only because of the expense of keeping up the cooling influence but because of the heat conveyed away by the cooling medium.

Attempts have been made" to construct rabble arms without artificial cooling equipment, dependence being placed upon the selection of a metal for the rabble arms capable of resisting very high temperatures, for 4D instance, a high-chromium steel alloy. But it was found that, owing to the low strength of the heat resistance alloy, at high temperatures and the high stresses set up by the heavy loads, both static and of torque, noncooling stirring devices made of such alloys failed in use. This failure is due partly to the employment of structural designs inadequate to meet the stresses encountered by the rabble arm in service at the high temperatures incident to the sintering operation, and partly because of the excessive heat conducted by the rabble arm beyond the furnace wall through which it must extend in receiving' its support and drive from exterior mechanism.

The present invention avoids the difficulties heretofore encountered, and provides a rabble arm of high temperature alloy adapted for overhead suspension, capable of withstanding the stresses encountered in use, notn withstanding the high temperature of the furnace, and one which avoids excessive conduction of heat through the .top wall of the furnace. To these ends, the invention proceeds upon the principle of constructing the rabble arm with its depending shaft member through which it is suspended and driven, and its laterally extending member which constitutes the sweep, of one single piece, preferably a casting of high temperature alloy; these members constituting hollow structures of relatively large internal dimensions with comparatively thin walls; the upper end of the shaft being formed with a bottle" neck shank which extends through the furnace arch for connection with the external supporting and driving mechanism; and the lateral member merging with the shaft member through means of a curved elbow con- 8 struction and tapering downwardly and outwardly from the dimensions of the shaft member, thereby producing a construction which, notwithstanding the reduced inherent strength of the metal at high temperatures, is peculiarly adapted to meet the stresses encountered by the rabble arm in use, which involve both torsional and bending moments in each member as well as a complication of these moments of stress at the elbow through which the two members merge.

ln the accompanying drawing, which illustrates the preferred embodiment of the invention by way of illustration- Figure l is a sideelevation of the rabble arm'with the'portion of the furnace arch with which it is concerned, shown in section.

Figure 2 is an elevation of the rabble arm as viewed from the right in Figure l; and

5 Figures Band l are, respectively, abot tom and a top plan view of the rabble arm.

l represents the vertical portion or column of the rabble arm,prov1ded at the top with a coupling flange 2, and 3 represents the latmembers are formed ino'ne pieceLa'nda'reL-fof hollow construction with large interior dimensions so that their walls, as indicated' in dotted lines, are thin comparedrwith their i overall transverse dimensions. ,'llhevmember 3 merges with the member l through an elbow construction 5, o, which VisV curved on the internal angle, the structurefmerges `from the hollow cylindrical depending shaft l to the downwardly Handi outwardly tapering 1 sweep member 3.

As shown in Figure 2, the base T of the vlat-verally extending vmember or sweep ie of materially yless transverse dimension than .L .EL 1.; v 'nti n .E the sha t l or even Aieuppei inneL poL ion ci the sweep', and is provided with marginal flanges 8 *having perforations 8a lthrough which the'rabble arm is adapted'toreceive the socalled blades or `other elements com- 73@ monly `,used withI rabble arms of this kind for stirrirngV up the-material. `'This construc-V tion Vof sweep member as will be .appreciated by comparing Figure 2 with Figure`` alg'- fords great strength and resistance to bending and torsional stresses encountered in use,

as well'asamplestrength vertically to resist bendinostresses )articularl at the elbow 5 6. v"Moreover tne construction einbodvinfr s i s IJv s;

as itldoes the Vrelativelylarge hollow shaft 40 l merging with the lhollow'downwar .ly and outwardly taperedswe'ep '3 through means of the' 'curved elbow,'r`esults in a very'strong and eicientstructure as a'whole under stresses necessarilyencountered in the rotation cfa verticalshaft'with a relatively longsweep extending laterally therefrom, 'and carrying stirring elements that drag through the 'mineral masscommonly'treatedwith the yuse' of rabble arms.. Coupling flange' 2 is of 'usual dimensionsl for-"attaching to standardizing driving mechanism for rabble arms infurnaces of the kind for which -thepresentinn vention is `intended, and beneath this Vcoupling flange andthe portion of the column l which passes throughthe arch A ofthe'furnace, Yis afreduced neck portion Il, which-is of quite suliicient stress-r'esisting capacity because 'of Vrelatively lower 'temperatures en- G0V countered` there, and which "thereby 4affords `the desired conditions' of 'reduced capacity for transmitting' heat '(convectio'nal 'transmission of heat ybeing largely choked by the bottle-neck construction, and heat rconduction Vbeing reduced bythe decreased section of the through which curvature 4ifreaeir/ metal); also, small subtraction of arch area, and standardized coupling facilities. Y

The main body of thecolumn or shaft and the laterally extending member have walls of such thickness combined with such relatively large sectional diameter as to make a strue- Y which encounter the 'higher temperati'ires incidentto its use, and 'with relativelysmall transverse dimensionsproviding 'chokage of' heat conductionand'convectioniand reduced .i

furnacefsurfa'ce interruption Yat the portion which passesthroughthe furnace-con- .linegsaid shaft having upon the upper: end

of said reduced portion, mea-ns for establishing suspending. and vdriving"connection with external-mechanism; and the laterally leX- ten'ding member being united-with the column orshaft through: a curved elbow and tapering downwardly` and outwardlyV therefrom. l 1 Y Y f2. A -non-lcooled, overhead suspension rabble V-a'rm Vfor furnaces, comprising'adependingshaft member constructed with-a vertical hollow body portion of relatively largedi-` ameter, an upper end portion of relatively smallerY diameter by which the shaft member-intersects the top con-fine of the furnace and' lthrough f which theA rabble arm l'is suspended' anddrivenwhen in service, and: a constricted free lower end; and a' laterally projecting hollow sweep memberha-vingfa relatively large downwardly inclined/and laterally tapered upperportion merging-at its inner end through curved continuingsurfaces, with major transversedimensionslof the body portion, and `having aA relatively narrow substantially horizontallower c p0rtion formed by A parallel 'vertical sides Lthat merge at their inner ends with the constrictedV free end of thefshaft member; thebottom confine off'said sweep comprisingga-substantiallyflat wall uniting the 'said sidesand havingflanges extending beyond the same.

. Signed at Ghicag'o, Illinois, this --19thvda'y of Septemfber,l928. c V y Y l A. 2FAI-lRENVALD.

relatively large fholf frio 

